A multi-mode optical waveguide can reduce a mode variance by having a refractive index distribution of decreasing in a core centrosymmetrically. The physical structure of the refractive index distribution depends on materials and production processes like the following conventional example.
A conventional graded-index optical waveguide is equipped with a predetermined mask for an optical medium, and gives a distribution to a refractive index of the optical waveguide by diffusing a diffusion source in the optical medium through an aperture of the mask (refer to, for example, Japanese Patent Laid-Open No. 57-198410 (page 2, FIG. 3); hereafter, this is called document 1).
In addition, there are also some which each radiate light to an optical medium, including monomer whose refractive index becomes small by photopolymerization, with being equipped with a mask with a predetermined transmittance, and give a distribution to a refractive index of an optical waveguide (refer to, for example, Japanese Patent Laid-Open No. 60-64310 (pages 2 to 3, FIG. 1): hereafter, this is called document 2).
Furthermore, there are also some which each are a method of utilizing the same photopolymerization reaction as that in document 2, and irradiate ultraviolet rays from two different directions to produce a waveguide lens which has a concentric refractive index distribution (refer to, for example, Japanese Patent Laid-Open No. 60-175010 (FIG. 7): hereafter, this is called document 3).
Moreover, there are also some which each are a method of utilizing the same photopolymerization reaction as that in document 2, and produce a graded-index waveguide by changing irradiation amount (refer to, for example, Japanese Patent Laid-Open No. 1-134310 (FIG. 1): hereafter, this is called document 4).
In addition, there are also some which each are equipped with a mask, which has a predetermined aperture portion, for optical plastics including metal salt of an organic carboxylic acid, and give a distribution to a refractive index of an optical waveguide by performing dipping in a solvent such as ethanol or acetone to diffuse the organic carboxylic acid outside (refer to, for example, Japanese Patent Laid-Open No. 60-188906 (pages 3 to 5, FIGS. 2 to 4): hereafter, this is called document 5).
On the other hand, surface mounting can be mentioned as the technology of low-cost and mass production of optical modules used for optical communication or optical networks.
This is the technology of producing external forms of a semiconductor laser and a lens, which are required for an optical module, with high precision beforehand, and performing passive alignment by arranging them in submicron accuracy on a silicon substrate in which a V-groove and the like are formed, or arranging alignment marks for positioning with high precision on optical components, fetching the alignment marks with a CCD camera or the like, and arranging them with applying image processing technology. In the case of passive alignment, since each optical component is arranged without monitoring light amount inputted into an optical fiber, the process tolerance and arrangement accuracy of these optical components affect the light amount finally inputted into the optical fiber. Therefore, it is necessary to process each optical component precisely and to align it with high precision.
In addition, in the case of a multimode optical fiber (hereafter, this is abbreviated as an MMF) such as a plastic fiber, there is no photodiode which has a light-receiving area corresponding to its large-diameter core, and there are also no peripheral parts such as a small and low-loss coupler which controls full modes. On the other hand, in the case of a single mode optical fiber (hereafter, this is abbreviated as an SMF), mode control is easy and a core diameter is also small, and hence, it is possible to obtain small and low-price peripheral parts.
By the way, among conventional optical modules, there are some which each use a thin film waveguide which has a grating coupler and a waveguide lens, and couple light, inputted into the thin film waveguide through the waveguide lens with the grating coupler, with an external optical component (refer to, for example, Japanese Patent Laid-Open No. 62-280827 (FIG. 1); hereafter, this is called document 6).
In addition, there are some which each are constituted of a V-groove group which is formed in parallel on a Si substrate, an optical fiber group positioned by the V-groove group, a light source group arranged in the same pitches, and a Fresnel lens group positioned by the V-groove group (refer to, for example, Japanese Patent Application Laid-Open No. 2004-109498 (FIG. 1); hereafter, this is called document 7).
Furthermore, there are those which each make highly precise optical axis adjustment unnecessary in the assembly of an optical module by using a graded index lens (GRIN lens) (refer to, for example, Japanese Patent Laid-Open No. 11-271575; hereafter, this is called document 8).
FIG. 29 shows a side view of a conventional optical module 610 shown in document 8.
The optical module 610 is constituted of an optical fiber 614 which is sandwiched between and held by quartz blocks 613 which are arranged through a spacer 612 on a substrate 611 and are vertically dividable, and serves as an optical waveguide, a laser diode 616 which is equipped with a terminal 616a which is fixed to a holder 615, provided on the substrate 611, and into which an electric signal is inputted, a GRIN lens 617 which is arranged between the quartz block 613 and laser diode 616, and is coupled to the optical fiber 614.
When an electric signal is inputted into the terminal 616a of the laser diode from the external, the laser diode 616 emits light or quenches light according to the status change of this electric signal, for example, ON/OFF of the signal. An optical signal which this laser diode 616 emits is converged by the GRIN lens 617 to be introduced into the optical fiber 614, and finally, is outputted into the external of the optical module 610.
Nevertheless, since it is necessary to inject diffusion material into an optical medium from the aperture of the mask, the conventional method in document 1 has a first subject that process becomes complicated by the supply of the diffusion material, the corruption by the diffusion material, and the like.
In addition, since it is necessary to perform the wet processing of performing the dipping of an optical plastic including the metal salt of an organic carboxylic acid at a solvent such as ethanol or acetone, the conventional method in document 5 has a first subject that process becomes complicated also in this case.
Furthermore, although the conventional methods in documents 2 to 4 each can produce a graded-index waveguide by the installation of the mask which adjusts a light amount, and the simple process of optical irradiation since polymerizing monomer in an optical medium by light changes a refractive index, it has a second subject that its heatproof temperature is 80° C. or less, and it has no heat resistance beyond 100° C., since an acrylic resin such as PMMA is used for the material made by a photopolymerization reaction. Hence, although it is satisfactory in an indoor environment, it cannot be used for outdoor use or a car for which the heat resistance of 100° C. or more is required.
In addition, since a grating coupler is required in order to couple with a thin film waveguide, the conventional method in document 6 has a third subject that complicated process is required and expensive and it cannot be achieved in low cost.
Furthermore, since a Fresnel lens corresponding to the diameter level of an optical fiber currently used is expensive, the conventional method in document 7 also has a third subject that it is unrealizable in low cost.
Moreover, although being low cost since a bulk type GRIN lens (aperture of 1 mm or more) is used, the conventional method in document 8 has a fourth subject that the miniaturization of an optical module cannot be performed.
In addition, in this specification, an optical fiber diameter level is defined as the size of being tenfold or less of optical fiber diameter.
Furthermore, although it is possible to produce a small waveguide type graded index lens, any one of the conventional methods shown in documents 2 to 4 has a fifth subject that a step of producing a waveguide type graded index lens becomes a step different from a step of producing an optical module using the produced waveguide type graded index lens. Since an expense which is required in manufacturing process influences cost since the waveguide type graded index lens is very small and the resin material cost occupying a manufacturing expense is extremely small, a production expense of the optical module becomes high cost when the step of producing the waveguide type graded index lens and the step of producing the optical module are different steps in this manner.
FIG. 28 is a structural diagram of a production apparatus 511 of a conventional optical waveguide described in document 3.
A mask 514 is installed on a surface (top face) of a high polymer film 513. Two change sections 514c which make ultraviolet rays 515 permeate are formed in parallel in a predetermined interval on this mask 514. The change portions 514c each have a distribution of transmittance of the ultraviolet rays 515 changing in a transverse direction, and are constituted so that the transmittance of the ultraviolet rays 515 may become zero at both ends and the largest in the center. Then, a pair of mirrors 516 and a prism 517 are provided above the mask 514, the prism 517 being provided in the center.
The parallel ultraviolet rays 515 are irradiated from a light source, and the ultraviolet rays 515 are divided into the right and the left by the prism 517, and are reflected by each of the pair of mirrors 516 to be irradiated on the mask 514 from two directions. The ultraviolet rays 515 penetrate only the change portions 514c of the mask 514 to proceed into the film 513, and the ultraviolet rays 515 permeating both the change portions 514c intersect in the film 513 to produce a circular exposed portion. This exposed portion becomes an optical waveguide 512.
Thus, the optical waveguide 512 is produced by irradiating ultraviolet rays on the film 513, polymerizing monomer in the film 513, and making a refractive index distribution formed.
Then, since it is necessary further to perform the separated process of producing an optical module using this optical waveguide 512 in order to complete an optical module, it becomes in high cost.
A first object of the present invention is to provide a manufacturing method of a graded-index optical member which produces the graded-index optical member in a simple process by forming a core section by changing a refractive index by an oxidation reaction caused by UV irradiation and heating using sheet-like polysilane.
In addition, a second object of the present invention is to provide a graded-index optical member which has the heat resistance of 100° C. or more by forming a core section by changing a refractive index by an oxidation reaction caused by UV irradiation and heating using sheet-like polysilane.
In addition, a third object of the present invention is to provide an optical module which is possible to make an optical module in low cost which uses the graded-index optical member of the present invention which is produced in the simple process of forming a core section by changing a refractive index by an oxidation reaction caused by UV irradiation and heating using a sheet-like base material whose main component is polysilane.
In addition, a fourth object of the present invention is to provide an optical module which is possible to make a small optical module which uses the small graded-index optical member of the present invention which is produced in the process of forming a core section by changing a refractive index by an oxidation reaction caused by UV irradiation and heating using a sheet-like base material whose main component is polysilane.
In addition, a fifth object of the present invention is to provide optical modules and the manufacturing methods of an optical module of the present invention each of which produces a waveguide type graded index lens and is able to fix an optical component at the same time.